The present invention relates generally to the field of medical isotopes production systems and extraction and purification processes therefore.
The primary target-irradiated, fission-produced molybdenum extractions and purification processes in use today are generally described in the 1998 IAEA report and a 2009 report published by the National Academies. In addition a detailed description of the Cintichem process may be found in the NEPA documentation associated with an earlier effort by the Department of Energy to make molybdenum-99 (Mo-99). These methodologies are summarized as follows.
At the National Institute for Radioelements IRE (Belgium) the following process is utilized: The targets are dissolved in sodium hydroxide (NaOH). Uranium (U) and fission products (FPs) precipitate out as hydroxides using a strong aqueous base (e.g., an approximately 10M solution NaOH). However, iodine (I) and Mo do not. The acidified solution causes iodine to be released and captured on a platinum-asbestos trap. The solution is then passed through an alumina column to capture Mo. Mo is then eluted via ammonium hydroxide (NH4OH). The Mo is then purified via ion-exchange resin (DOWEX®). The solution is then acidified with sulfuric acid (H2SO4) and passed through activated carbon.
At Mallinckrodt Baker (Netherlands), the following process is utilized: The targets are dissolved in NaOH. Mo and many other FPs are absorbed on an AG 1-X8 column. Next, Mo and other FPs are eluted off the AG 1-X8 columns with sulfuric acid. Then the acidified solution enters ion-exchange column (SM-7) to retain iodine. The acidified solution then enters a magnesium dioxide (MnO2) column and is purified from FPs via a chromatography method (the molybdenum remains on the column). The MnO2 column is then dissolved in H2SO4. The molybdenum is then captured on a CHELEX® resin column. Next, the molybdenum is eluted with NH4OH. The molybdenum then undergoes final purification via sublimation.
At NTP Radioisotopes (South Africa), the following process is utilized: The targets are dissolved in NaOH. Uranium and most FPs precipitate out as hydroxides, Mo does not. The solution then goes through two unspecified anion exchange columns—both eluted via unspecified solution. Next, the solution goes through a final chelating resin and is eluted with NH4OH. The NH4OH eluate is filtered and evaporated. A residue containing Mo is re-dissolved with NaOH to convert the Mo to molybdate.
At the Karpov Institute of Physical Chemistry (Russia), the following procedure is utilized: The targets are dissolved in nitric acid (HNO3) and FP gases are captured and held. Molybdenum and a few other FPs are separated into an organic phase; most of the U and FPs remain in the aqueous phase. Next a “re-extraction” step is performed (the molybdenum is in the aqueous phase, the remaining U and FPs are in the organic phase). Then the aqueous molybdenum-containing solution is passed through a non-specified chromatographic column. The aqueous solution is then evaporated. The molybdenum-containing residue is then dissolved in either an acid or an alkali solution.
In the ANSTO LEU process (Australia), the targets are first dissolved in HNO3. The solution is passed through an alumina sorbent column. The alumina column is then washed with nitric acid, water and a dilute ammonia solution. The molybdenum is eluted from the column with concentrated ammonia solution. The solution is then boiled to remove iodine and ruthenium. The Karlsruhe LEU process (Germany) is generally similar to the Mallinckrodt process. The process followed by CNEA (Argentina) is thought to be similar to the Mallinckrodt process.
The Cintichem process (United States) may be broken down into an extraction phase and a purification phase. In the extraction phase, first, the target is dissolved in nitric acid & sulfuric acid. Small amounts of sodium iodide (NaI), silver nitrate (AgNO3), and hydrochloric acid (HCl) are added to precipitate iodine. Molybdenum is added to the carrier solution. Next an oxidizing agent (KMnO4) is added. Carriers for rhodium and ruthenium are added. Molybdenum is precipitated with benzoin-α-oxime and filtered from the solution. Multiple acid rinse and filtration steps are then performed to capture a maximum amount of the molybdenum.
In the purification phase, there is a repeated washing of the filter cake with H2SO4 which still contains the iodine previously precipitated. It is then dissolved in NaOH and hydrogen peroxide H2O2 (an oxidizing agent). The solution is then purified via silver (Ag) on charcoal column (this removes the iodine). A second iodine precipitation is conducted. The solution is then filtered through a column containing silver on charcoal, hydrated zirconium oxide, and activated charcoal. The final solution is then filtered through a micron filter. It is believed that MDS Nordion (Canada) follows the Cintichem process.
U.S. Pat. No. 5,596,611 to Ball discloses a uranyl nitrate homogeneous reactor (100 kW to 300 kW) for the production of molybdenum-99. The reactor is immersed in a containment pool which serves as a heat removal media for the sensible and decay heat generated in the reactor. The reactor vessel is finned to enhance the heat transfer to the containment pool. The reactor operates in a continuous mode in which the radioactive waste products are re-circulated back into the reactor. A portion of the uranyl nitrate solution from the reactor is directly siphoned off and passed through columns of alumina to fix some of the fission products, including Mo-99, on the alumina. The Mo-99 and some fission products on the alumina column are then removed through elution with a hydroxide and the Mo-99 is either precipitated out of the resultant eluate with benzoin-α-oxime or passed through other columns.
In addition, U.S. Pat. No. 5,508,010 and United States Patent Application Publication No. 2010/0202943 A1 generally describe processes in which the isotope Mo-99 is separated from an aqueous solution containing a mixture of nuclear fission products.
The above processes suffer from various drawbacks due to processing inefficiencies, inefficiencies in the utilization of time and/or materials, and/or require the unnecessary consumption of operator time and attention. As such, there is a need in the art for an efficient molybdenum-99 extraction and purification method and apparatus.